Counterflow heat exchanger

ABSTRACT

A counterflow heat exchanger of the Z-flow or U-flow type in which the flow passage heights of each fluid are varied so as to minimize pressure drop.

United States Patent Inventors John L. Mason Palos Verdes Estates;Robert W. Greenwood, Redondo Beach, both of Calif. App]. No. 853,248Filed Aug. 27, 1969 Patented Oct. 19, 1971 Assignee The GarrettCorporation Los Angeles, Calif.

COUNTERFLOW HEAT EXCHANGER 16 Claims, 9 Drawing Figs.

US. Cl 165/166, 165/ 146 Int. Cl F281 3/00 Field of Search 165/146, 147,166 MP References Cited UNITED STATES PATENTS 3,165,152 1/1965 Jones165/166 3,228,464 1/1966 Steirn et a1. 165/166 3,282,334 11/1966Stahlberger 165/166 3,322,189 5/1967 Tobouzian..... 165/166 X 3,508,6074/1970 Hermann 165/166 X Primary ExaminerFrederick L. Matteson AssistantExamiher-Theophil W. Streule Attorneys--Albert .1. Miller and John N.Hazelwood ABSTRACT: A counterflow heat exchanger of the Z-flow or U-flowtype in which the flow passage heights of each fluid are varied so as tominimize pressure drop.

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A ORNEY COUNTERFLOW I-IEA'll EXCHANGER BACKGROUND OF THE INVENTION Acounterflow heat exchanger has the most efficient flow arrangement inthat it most efiiciently utilizes the available temperature differentialbetween the two working fluids. This type of flow arrangement is,however, especially awkward to manifold, particularly in a gas-to-gasheat exchanger.

One end section treatment for a gas-togas counterflow heat exchangerthat has been developed to facilitate manifolding is the so-calledZ-flow configuration. In the Z-flow heat exchanger, two fluids flow inadjacent uniform height passages separated by plates and closed by barslocated as required at the edges of the passages. The first fluid flowsdirectly across the heat exchanger from one manifold to a manifold onthe opposite side of the heat exchanger. The second fluid enters theheat exchanger at a right angle to the flow of the first fluid, is thedirected counter to the flow of the first fluid and finally out theopposite side of the heat exchanger again at a right angle to the flowof the first fluid. These changes in direction of the flow of the secondfluid give rise to the Z-flow designation.

Since however, the crossflow sections (at right angles) of the Z-flowheat exchanger are inherently long and narrow, the pressure drop of thesecond fluid in these sections is excessive. Attempts to reduce thepressure drop in these sections have resulted in decreasing thecounterflow character of the heat exchanger (hence its efficiency)and/or excessive increases in the pressure drop for the first fluid.

Other counterflow heat exchanger configurations, such as the U-flow typein which one of the fluids flows in a substantially U-shaped pattern,are likewise faced with the same inherent problems as the Z-shapedconfiguration.

SUMMARY OF THE INVENTION The present invention is an improvedcounterflow heat exchanger which reduces the pressure drop through thecrossflow sections of the heat exchanger without reducing thecounterflow nature of the heat exchanger or introducing excessivepressure drops elsewhere in the heat exchanger. The height of the Z-flowor U-flow passages is varied to provide a greater height in thecrossflow sections than in the counterflow section. The height of thecorresponding straight-through flow passages is likewise varied tocompensate for the height variations in the Z-flow or U-flow passages.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of theassembled heat exchanger of the present invention.

FIG. 2 is a perspective view of a single Z-flow passage of the assembledheat exchanger of FIG. 1.

FIG. 3 is a perspective view of a single straight-through flow passageof the assembled heat exchanger of FIG. 1.

FIG. 4 is an enlarged partial section view of the assembled heatexchanger of FIG. I taken along line 4-4 of FIG. 1.

FIG. 5 is a schematic plan view of the assembled heat exchanger of FIG.1 illustrating the fluid manifolding.

FIG. 6 is a perspective view of a modified Z-flow passage.

FIG. 7 is a perspective view of a modified straight-through flow passagecomplementary to the Z-flow passage of FIG. 6.

FIG. 8 is a perspective view,- partially cut away of an alternateassembled heat exchanger of the present invention.

FIG. 9 is an enlarged partial sectionview of the assembled heatexchanger of FIG. 8 taken along line 9-9 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An assembled counterflow heatexchanger of the present invention is illustrated in FIG. I. This heatexchanger I0 comprises a series of alternate Z-flow passages 12 andstraightthrough flow passages 14. The plurality of passages 12 and I4are assembled between a heat exchanger top plate 16 and bottom plate I8.The entire assembly I0 may be brazed together by conventional brazingtechniques.

A single Z-flow passage is shown in FIG. 2. This passage includes atriangular crossflow inlet section 22 having fins 24 running in thedirection of fluid flow, a parallelogram counterflow section 26 havingoffset corrugated fins 28 and a triangular crossflow outlet section 30having fins 32 in the direction of fluid flow. As indicated, the heightof the crossflow sections 22 and 30 is greater than the counterflowsection 26. An inlet header bar 34 closes the inlet end of the passageexcept for the crossflow inlet section 22 while an outlet header bar 36closes the outlet end of the passage except for the crossflow outletsection 30. Side header bars 38 and 40 extend along both sides of thepassage. A passage separator plate 42 is shown over the passage. toserve as a means to separate flow in adjacent passages.

FIG. 3 illustrates a single straight-through flow passage which includesa triangular crossflow inlet section 44 having fins 46 extending in thedirection of fluid flow, a central parallelogram counterflow section 4%with offset corrugated fins 50, and a triangular crossflow outletsection 52 having fins 54 in the direction of fluid flow. The triangularinlet section 44,

centralparallelogrant section 48, and triangular outlet section 52 ofthe straight-through flow passage are adapted to correspond to thecrossflow outlet section 30, parallelogram counterflow section 26 andcrossflow inlet section 22 respectively of the Z-flow passages.Accordingly, the two triangular sections 44 and 52 are not as high asthe central section 48 so as to accommodate the greater height of thecrossflow sections 22 and 30 of the Z-flow passage when passages 12 andI4 are assembled into the heat exchanger 10. A passage separator plate56 would be required between the top of the straightthrough flow passage14 and the bottom of the adjacent Z- flow passage 12. End header bars 58and 60 extending across the entire end are also required for thestraight-through flow passage.

The heat exchanger 10 is formed of a stack of alternating passages 12and I4 separated by plates 42 and 56. The varying heights of therespective passage sections are shown in FIG. 4. While not required, thehot fluid to be cooled will normally flow through the Z-flow passage 12while the coolant will normally flow through the straight-throughpassage 14.

Manifolding for the heat exchanger 10 is conventional for a Z-type heatexchanger as shown schematically in FIG. 5. The Z-flow inlet manifold 62which receives a heated fluid to be cooled communicates with the inletcrossflow section 22 of the stacked Z-flow passages 12. The heated fluidis prevented from entering the stacked straight-through passages 14 bythe end header bars 60. The heated fluid proceeds through the crossflowinlet section 22 which distributes the fluid at various points to thecounterflow section 26 which in turn passes the then cooled fluid to thecrossflow outlet section 30. A Z-flow outlet manifold 64 collects thefluid from the Z-flow outlet sections 30 of the stacked Z-flow outletpassages 12. The coolant flows from the straight-through flow inletmanifold 66 through the straight-through flow passages 14, then out thestraight-through flow outlet manifold 68.

Since the crossflow inlet and outlet sections 22 and 30 are relativelylong and narrow, the fins therein, 24 and 32 are relativelynonrestrictive and the height of these two sections has been increasedrelative to the counterflow section 26 which includes more extensivefins 28 designed for greater heat transfer. The triangular sections 44and 52 of the straightthrough passages 14 likewise have less restrictivefins 46 and 54 than the fins 50 in the central parallelogram section 48.

A modified Z-flow type heat exchanger can be formed of alternatepassages of the Z-flow passage of FIG. 6 and the straight-through flowpassage of FIG. 7. In this variation the counterflow sections 26' and48' respectively are substantially rectangular rather than configured asa parallelogram. This embodiment provides a somewhat greater counterflowheat exchanger area than the basic Z-flow configuration of FIGS. 2 and3.

In the Z-flow passage of FIG. 6, the height of the crossflow sections22' and 30' having fins 24' and 32' respectively is greater than thecounterflow section 26' having fins 28'.

Header bars 26', 36', 38', and 40' are provided as in the basic Z-flowconfiguration.

Likewise, the straight-through flow passage includes a counterflowsection 48 having fins 50' whose height is greater than the crossflowsection 44' and 52' having fins 46 and 54 respectively. Also headers 58'and 60' are provided.

An alternate end section treatment for a counterflow heat exchanger isthe so-called U-flow configuration illustrated in FIGS. 8 and 9. Theheat exchanger is comprised of an alternating stacked series of U-flowpassages 72 and straight-through flow passages 74.

The straight-through flow passage 74 comprises a triangular crossflowinlet section 76 having fins 78 extending in the direction of fluidflow, a central rectangular counterflow section 80 with offsetcorrugated fins 82 and a triangular crossflow outlet section 84 havingfins 86. End header bars 85 and 87 extend across the front and backrespectively of each passage 74.

The U-flow passage 72 includes a triangular crossflow inlet section 88having fins 90 extending in the direction of fluid flow, a centralrectangular counterflow section 92 having offset corrugated fins 94 anda triangular crossflow outlet section 96 having fins 98 in the directionof the fluid flow. lnlet side header bar 100, end header bars 104, andoutlet side header bar 102 together with passage separator plates 108and 110 confine the fluid flow to the individual passages. A top plate106 and bottom plate (not shown) confine the stacked passages of theheat exchanger.

As clearly indicated in FIG. 9, the height of the crossflow inlet andoutlet sections 90 and 98 of the U-flow passage 72 is greater than theheight of the counterflow section 92 of this passage. correspondingly,the crossflow sections 76 and 84 of the straight-through passage 74 havea lesser height than the central counterflow section 80. Manifolding ofthe U-flow configuration would be similar to that for the Z-flowconfiguration except that both the inlet and outlet manifold for the U-flow passages will be at the same end of the heat exchanger rather thanat opposite ends.

The counterflow heat exchangers described above reduces the pressuredrop of the fluid in previously high pressure drop sections of the heatexchanger without significantly decreasing the counterflow nature of theheat exchanger or excessively increasing the pressure drop in other ofthe heat exchanger sections.

While specific embodiments of the invention have been illustrated anddescribed, it is to be understood that these embodiments are provided byway of example only and that the invention is not to be construed asbeing limited thereto, but only by the proper scope of the followingclaims.

We claim:

1. A heat exchanger comprising:

a plurality of first formed plates having a raised central portion;

a plurality of second formed plates having a depressed central portioncorresponding to the raised central portion of said first formed plates;

said first formed plates and said second formed plates alternatelydisposed in a spaced, substantially parallel, relation to alternatelyform first fluid flow passages and second fluid flow passages in a heattransfer relationship;

said first passages having an upper first formed plate and a lowersecond fonned plate to form an inlet section, an outlet section, andcentral section, said central section formed by the raised centralportion of said upper first formed plate and the depressed centralportion of said lower second formed plate to have a flow height greaterthan the inlet and outlet sections;

said second passages having an upper second formed plate and a lowerfirst formed plate to form an inlet section in a crossflow heat transferrelationship with the outlet section of said first passages, an outletsection in a crossflow heat transfer relationship with the inlet sectionof said first passages, and a central section in a counterflow heattransfer relationship with the central section of said first passages,said central section of said second passages formed by the depressedcentral portion of said upper second formed plate and the raised centralpotion of said lower first formed plate to have a flow height less thanthe inlet and outlet sections of said second passages.

2. The heat exchanger of claim 1 wherein the combined fluid flow heightof the first passage inlet section plus the second passage outletsection equals the combined fluid flow height of the first passagecentral section plus the second passage central section equals thecombined fluid flow height of the first passage outlet section plus thesecond passage inlet section.

3. The heat exchanger of claim 1 wherein said inlet and outlet sectionsof said first and second passages are substantially triangular and saidcentral sections of said first and second passages are substantiallyparallelogrammic.

4. The heat exchanger of claim 3 wherein said central sections of saidfirst and second passages are substantially rectangular.

5. The heat exchanger of claim 3 wherein the fluid flow in said firstpassages is substantially straight through and the fluid flow in saidsecond passage 5 is substantially U-shaped 6. The heat exchanger ofclaim 14 wherein said central sections of said first and second passagesare substantially rectangular.

7. The heat exchanger of claim 14 wherein the fluid flow in said firstpassages is substantially straight through and the fluid flow in saidsecond passages is substantially U-shaped.

8. The heat exchanger of claim 3 wherein the fluid flow in said firstpassages is substantially straight through and the fluid flow in saidsecond passages is substantially Z-shaped.

9. The heat exchanger of claim 8 wherein the inlet, outlet, and centralsections of said first and second passages include heat transfersurfaces disposed therein, said heat transfer surfaces in said centralsections substantially more restrictive to fluid flow than the heattransfer surfaces of said inlet and outlet sections.

10. A heat exchanger comprising:

a plurality of substantially rectangular first formed plates having araised parallelogrammic central portion;

a plurality of substantially rectangular second formed plates having adepressed parallelogrammic central portion corresponding to the raisedcentral portion of said first formed plates,

said first formed plates and said second formed plates al ternatelydisposed in a spaced, substantially parallel, relation to alternatelyform first fluid flow passages and second fluid flow passages in a heattransfer relationship;

said first passages having an upper first formed plate and a lowersecond formed plate to form a triangular inlet section, a triangularoutlet section, and a parallelogrammic central section, said centralsection formed by the raised parallelogrammic central portion of saidupper first formed plate and the depressed parallelogrammic centralportion of said lower formed plate to have a flow height greater thanthe inlet and outlet sections, said first passages including edgeclosure elements disposed between said upper first formed plate and saidlower second formed plate at the two short sides thereof;

said second passages having an upper second formed plate and a lowerfirst formed plate to form a triangular inlet section in a crossflowheat transfer relationship with the triangular outlet section of saidfirst passages, a triangular outlet section in a crossflow heat transferrelationship with the triangular inlet section of said first passages,and a parallelogrammic central section in a counterflow heat transferrelationship with the parallelogrammic central section said firstpassages, said second passage central section formed by the depressedparallelogrammic central portion of said upper second formed plate andthe raised parallelogrammic central portion of said lower first formedplate to have a flow height less than the inlet and outlet section ofsaid second passages, said second passages including long side edgeclosure elements disposed between the two long side edges of said uppersecond formed plate and said lower first formed plate and short sideedge closure elements disposed between a portion of each of the twoshort side edges of said upper second formed plate and said lower firstformed plate.

II. The heat exchanger of claim and in addition a first passage inletmanifold disposed along the inlet section long side of said firstpassages to provide fluid to said first passage inlet sections, a firstpassage outlet manifold disposed along the outlet section long side ofsaid first passages to receive fluid from said first passage outletsections, a second passage inlet manifold disposed along the portion ofthe inlet section short side of said second passages not closed by theshort side edge closure elements to provide fluid to said second passageinlet sections, and a second passage outlet manifold disposed along theportion of the outlet section short side of said second passages notclosed by the short side edge closure elements to receive fluid fromsaid second passage outlet sections.

12. A heat exchanger comprising:

a plurality of first fluid passages for the flow of a first fluid;

a plurality of second fluid passages for the flow of a second fluid at atemperature different from said first fluid, said second fluid passagesalternating with said first passages in a heat transfer relationship inthe heat exchanger;

said first fluid passages having an inlet section at one end, an outletsection at the other end and an central section disposed between saidinlet and outlet sections, said central section having a flow heightgreater than the inlet and outlet sections;

said second fluid passages having an inlet section in a crossflow heattransfer relationship with the outlet section of said first passages, anoutlet section in a crossflow heat transfer relationship with the inletsection of said first passages, and a central section in a counterflowheat transfer relationship with the central section of said firstpassages, said second passage central section having a flow height lessthan the inlet and outlet sections of said second passages.

13. The heat exchanger of claim 12 wherein the combined fluid flowheight of the first passage inlet section plus the second passage outletsection equals the combined fluid flow height of the first passagecentral section plus the second passage central section equals thecombined fluid flow height of the first passage outlet section plus thesecond passage inlet section.

M. The heat exchanger of claim 12 wherein said inlet and outlet sectionsof said first and second passages are substantially triangular and saidcentral sections of said first and second passages are substantiallyparallelogrammic.

15. The heat exchanger of claim 14 wherein the fluid flow in said firstpassages is substantially straight through and the fluid flow in saidsecond passages is substantially Z-shaped.

H6. The heat exchanger of claim 15 wherein the inlet, outlet, andcentral sections of said first and second passages include heat transfersurfaces disposed therein, said heat transfer surfaces in said centralsections substantially more restrictive to fluid flow than the heattransfer surfaces of said inlet and outlet sections.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,611,782 DatedOctober 19, 1971 Inventor(s) John L. Mason and Robert W.Greenwood It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Claim 5, line 3, change "passage 5" to --passages-- after "shaped" addSigned and sealed this 13th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. A heat Exchanger comprising: a plurality of first formed plateshaving a raised central portion; a plurality of second formed plateshaving a depressed central portion corresponding to the raised centralportion of said first formed plates; said first formed plates and saidsecond formed plates alternately disposed in a spaced, substantiallyparallel, relation to alternately form first fluid flow passages andsecond fluid flow passages in a heat transfer relationship; said firstpassages having an upper first formed plate and a lower second formedplate to form an inlet section, an outlet section, and central section,said central section formed by the raised central portion of said upperfirst formed plate and the depressed central portion of said lowersecond formed plate to have a flow height greater than the inlet andoutlet sections; said second passages having an upper second formedplate and a lower first formed plate to form an inlet section in acrossflow heat transfer relationship with the outlet section of saidfirst passages, an outlet section in a crossflow heat transferrelationship with the inlet section of said first passages, and acentral section in a counterflow heat transfer relationship with thecentral section of said first passages, said central section of saidsecond passages formed by the depressed central portion of said uppersecond formed plate and the raised central potion of said lower firstformed plate to have a flow height less than the inlet and outletsections of said second passages.
 2. The heat exchanger of claim 1wherein the combined fluid flow height of the first passage inletsection plus the second passage outlet section equals the combined fluidflow height of the first passage central section plus the second passagecentral section equals the combined fluid flow height of the firstpassage outlet section plus the second passage inlet section.
 3. Theheat exchanger of claim 1 wherein said inlet and outlet sections of saidfirst and second passages are substantially triangular and said centralsections of said first and second passages are substantiallyparallelogrammic.
 4. The heat exchanger of claim 3 wherein said centralsections of said first and second passages are substantiallyrectangular.
 5. The heat exchanger of claim 3 wherein the fluid flow insaid first passages is substantially straight through and the fluid flowin said second passage 5 is substantially U-shaped
 6. The heat exchangerof claim 14 wherein said central sections of said first and secondpassages are substantially rectangular.
 7. The heat exchanger of claim14 wherein the fluid flow in said first passages is substantiallystraight through and the fluid flow in said second passages issubstantially U-shaped.
 8. The heat exchanger of claim 3 wherein thefluid flow in said first passages is substantially straight through andthe fluid flow in said second passages is substantially Z-shaped.
 9. Theheat exchanger of claim 8 wherein the inlet, outlet, and centralsections of said first and second passages include heat transfersurfaces disposed therein, said heat transfer surfaces in said centralsections substantially more restrictive to fluid flow than the heattransfer surfaces of said inlet and outlet sections.
 10. A heatexchanger comprising: a plurality of substantially rectangular firstformed plates having a raised parallelogrammic central portion; aplurality of substantially rectangular second formed plates having adepressed parallelogrammic central portion corresponding to the raisedcentral portion of said first formed plates, said first formed platesand said second formed plates alternately disposed in a spaced,substantially parallel, relation to alternately form first fluid flowpassages and second fluid flow passages in a heat transfer relationship;said first passages having an upper first formed plate and a lowersecond formed plate to form a triangular inlet section, a triaNgularoutlet section, and a parallelogrammic central section, said centralsection formed by the raised parallelogrammic central portion of saidupper first formed plate and the depressed parallelogrammic centralportion of said lower formed plate to have a flow height greater thanthe inlet and outlet sections, said first passages including edgeclosure elements disposed between said upper first formed plate and saidlower second formed plate at the two short sides thereof; said secondpassages having an upper second formed plate and a lower first formedplate to form a triangular inlet section in a crossflow heat transferrelationship with the triangular outlet section of said first passages,a triangular outlet section in a crossflow heat transfer relationshipwith the triangular inlet section of said first passages, and aparallelogrammic central section in a counterflow heat transferrelationship with the parallelogrammic central section said firstpassages, said second passage central section formed by the depressedparallelogrammic central portion of said upper second formed plate andthe raised parallelogrammic central portion of said lower first formedplate to have a flow height less than the inlet and outlet section ofsaid second passages, said second passages including long side edgeclosure elements disposed between the two long side edges of said uppersecond formed plate and said lower first formed plate and short sideedge closure elements disposed between a portion of each of the twoshort side edges of said upper second formed plate and said lower firstformed plate.
 11. The heat exchanger of claim 10 and in addition a firstpassage inlet manifold disposed along the inlet section long side ofsaid first passages to provide fluid to said first passage inletsections, a first passage outlet manifold disposed along the outletsection long side of said first passages to receive fluid from saidfirst passage outlet sections, a second passage inlet manifold disposedalong the portion of the inlet section short side of said secondpassages not closed by the short side edge closure elements to providefluid to said second passage inlet sections, and a second passage outletmanifold disposed along the portion of the outlet section short side ofsaid second passages not closed by the short side edge closure elementsto receive fluid from said second passage outlet sections.
 12. A heatexchanger comprising: a plurality of first fluid passages for the flowof a first fluid; a plurality of second fluid passages for the flow of asecond fluid at a temperature different from said first fluid, saidsecond fluid passages alternating with said first passages in a heattransfer relationship in the heat exchanger; said first fluid passageshaving an inlet section at one end, an outlet section at the other endand an central section disposed between said inlet and outlet sections,said central section having a flow height greater than the inlet andoutlet sections; said second fluid passages having an inlet section in acrossflow heat transfer relationship with the outlet section of saidfirst passages, an outlet section in a crossflow heat transferrelationship with the inlet section of said first passages, and acentral section in a counterflow heat transfer relationship with thecentral section of said first passages, said second passage centralsection having a flow height less than the inlet and outlet sections ofsaid second passages.
 13. The heat exchanger of claim 12 wherein thecombined fluid flow height of the first passage inlet section plus thesecond passage outlet section equals the combined fluid flow height ofthe first passage central section plus the second passage centralsection equals the combined fluid flow height of the first passageoutlet section plus the second passage inlet section.
 14. The heatexchanger of claim 12 wherein said inlet and outlet sections of saidfirst and second passages are substantially triangular and said centralsections of said first and second passages are substantiallyparallelogrammic.
 15. The heat exchanger of claim 14 wherein the fluidflow in said first passages is substantially straight through and thefluid flow in said second passages is substantially Z-shaped.
 16. Theheat exchanger of claim 15 wherein the inlet, outlet, and centralsections of said first and second passages include heat transfersurfaces disposed therein, said heat transfer surfaces in said centralsections substantially more restrictive to fluid flow than the heattransfer surfaces of said inlet and outlet sections.